1. Field of the Invention:
This invention relates to soybean saponins, their uses, and a method of isolating the same. More particularly, this invention is concerned with novel saponins separated from soybeans, metabolism affecting and antioxidizing compositions containing as an effective component a saponin which can be separated from soybeans, and a method of separating saponins from soybeans.
2. Description of the Prior Art:
It is known that various kinds of sapnonins occur in plants and animals, and that soybeans contain certain kinds of saponins, too. The soybean saponins are known to give by hydrolysis five kinds of sapogenols called soya sapogenols A, B, C, D and E, and three compounds giving soya sapogenol B, i.e., soya saponins I, II and III, are known by their chemical structures [see, for example, Chem. Pharm. Bull., 24(1), 121-129 (1978)]. It is known that these soya saponins are physiologically active in causing hemolysis, and killing fishes and insects [see I. E. Liener, "Toxic Constituents of Plant Foodstuffs", Academic Press, New York, 169 (1969)]; I. Ishaaya, Y. Birk, A. Bondi and Y. Tencer, J. Sci. Food Agr., 20,433 (1969) [C.A., 71, 89173 (1969)]; H. C. F. Su, R. D. Speirs and P. G. Mahany, J. Econ. Entomol., 65, 844 (1972) [C.A., 77, 84473 (1972)]; Y. Birk, A. Bondi, B. Gestetner and I. Ishaaya, "A Thermostable Hemolytic Factor in Soybeans", Nature, 197, 1089 (1963); or the like].
It is, however, believed that it is not known that saponins extracted from soybeans have a vital metabolic action, particularly for the inhibition of formation of lipid peroxides, and the promotion of metabolism of lipids and uric acid, and an antioxidizing action for food, or the like.
As is well known, the existence of lipid peroxides is very harmful to the human body. Serious attention has come to be paid to the relation between ageing and lipid peroxides, since J. Glavind et al. reported the existence of lipid peroxides in atherosclerotically hardened aortic lipids, and the presence of a mutual relationship between the degree of change in morbidity and the quantity of lipid peroxides [Acta Pathol. Microbiol. Scand., 30, 1 (1952)]. Aoyama et al. reported that arteriosclerosis would be caused by lipid peroxides [Jap. Heart J., 6, 128 (1965)]. Fukuzumi et al. reported that lipid peroxides had been found in the wall of the aorta in the chest of a man suffering from atherosclerosis, but that no lipid peroxide had been found in any normal aorta [Oil Chemistry, 10, 659 (1961); 12, 93 (1963); and 14, 119 (1965)]. Fukuzumi et al. also recognized the existence of conjugated diene hydroperoxides of fatty acids in cancerous tissues [Oil Chemistry, 10, 643 (1961); and 12, 165 (1963)]. Iizuka discussed the pathological significance of autoxidation in the formation of a cerebral tumor [Brains and Nerves, 14, 405 (1962)]. The toxic action of increased lipid peroxides on the living organisms was attributed, for example, to their relation to .beta.-lipoproteins [Nishida et al., J. Lipid Res., 1, 450 (1960)], or the trouble which they might cause to the --SH groups in enzyme proteins [E. D. Wills, Biochem. Pharmacol., 7, 7 (1961)].
It is also known that lipid peroxides destroy various kinds of vitamins and cause trouble in the metabolism of fatty acids, leading to obesity. In the event lipid peroxides are formed by autoxidation of fatty acids, vitamin E (.alpha.-tocopherol) is known as an effective agent for inhibiting the formation of lipid peroxides to thereby prevent ageing. Vitamin E is, however, very expensive, and as it is insoluble in water and soluble in oil, it is stored in the body for a long period of time, and produces side effects. Vitamin B.sub.2 (riboflavin) having no such disadvantage is, therefore, sometimes used, but disadvantageously has an extremely lower power of inhibiting the formation of lipid peroxides than vitamin E. It has, thus, been desired to develop a medicine which is inexpensive, soluble in water, safe to use, and has a high power of inhibiting the formation of lipid peroxides.
It is also well known that if oils and fats are left as they are, they are oxidized, and that the increased peroxides cause the so-called oil burning which lowers their flavor sharply. A variety of antioxidizing agents are usually employed for preserving food, cosmetics, or the like. Most of those antioxidizing agents are, however, chemically synthesized products, and it is not recommendable from the standpoint of safety to use them continuously for a long period of time. It has, therefore, been desired to develop a safer antioxidizing agent composed of a natural substance which can be derived from the food which one eats in his daily life.